scholarly journals Fe-Ti Oxide Assemblages from the Contact-Metamorphosed Mafic-Ultramafic Rocks of the Sedova Zaimka Intrusion (Western Siberia, Russia): The Tracking of Metamorphic Transformations

Minerals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 253 ◽  
Author(s):  
Tatyana V. Svetlitskaya ◽  
Peter A. Nevolko ◽  
Pavel A. Fominykh
Keyword(s):  
Western Siberia ◽  
Amphibolite Facies ◽  
Contact Metamorphism ◽  
Ultramafic Rocks ◽  
Granite Pluton ◽  
Silicate Minerals ◽  
Elevated Content ◽  
Unstable Phase ◽  
Metamorphic Fluids ◽  
Oxide Minerals

Studies that track and compiled transformations of ilmenite and magnetite under conditions of different metamorphic grades are still very limited. The Sedova Zaimka intrusion in Western Siberia (Russia) is a good example to examine the effect of contact metamorphism from greenschist to low-amphibolite facies on magmatic Fe-Ti oxide minerals, as this small mafic-ultramafic body is located within contact metamorphic aureole of a large granite pluton. In the Sedova Zaimka, ilmenite with little to no magnetite is present as an accessory dissemination throughout metamorphosed rocks. Ilmenite is variably enriched in MnO (1 to 13.3 wt%) and depleted in MgO (less than 0.3 wt%), suggesting that its primary magmatic composition has been unevenly modified by diffusion re-equilibrium with coexisting metamorphic silicates. The elevated content of ZnO (up to 0.5 wt%) and NiO (up to 0.4 wt%) in ilmenite suggests that both ZnO and NiO, like MnO, must be strongly partitioned into ilmenite relatively to silicate minerals under the reducing contact metamorphic conditions, if chromite is absent. The textural observations of ilmenite–sulfide and ilmenite–titanite–sulfide relationships indicate that Ti-magnetite, in contrast to ilmenite, is an unstable phase in the presence of sulfur-rich reduced metamorphic fluids and is completely replaced by sulfides, with the development of specific “octahedral meshes” of ilmenite in sulfides.

Apatite composition and the fugacities of HF and HC1 in metamorphic fluids

1985 ◽  
Vol 49 (350) ◽  
pp. 77-79 ◽  
Author(s):  
Bruce W. D. Yardley
Keyword(s):  
Experimental Data ◽  
Amphibolite Facies ◽  
Lower Grade ◽  
Two Samples ◽  
Metamorphic Fluids ◽  
Independent Estimate ◽  
Grade Rock ◽  
Acceptable Agreement

AbstractMicroprobe analyses of the halogen contents of apatites from two samples of amphibolite-facies schist from Connemara, Ireland, have been used to calculate the fugacity ratios fHCl/fH2O and fHF/fH2O using the experimental data of Korzhinskiy. The results imply fugacities for both acids in the range 0.03 to 0.1 bars, but whereas for the lower grade rock fHF > fHCl, the migmatitic sample gives fHF⋍fHCl. An independent estimate of fHF/fH2O from the biotite composition in one sample is in acceptable agreement with the result obtained from apatite.

scholarly journals Early (3700 Ma) Archaean rocks of the Isua supracrustal belt and adjacent gneisses

1983 ◽  
Vol 112 ◽  
pp. 5-22
Author(s):  
A.P Nutman ◽  
D Bridgwater ◽  
E Dimroth ◽  
R.C.O Gill ◽  
M Rosing
Keyword(s):  
Amphibolite Facies ◽  
Iron Formation ◽  
Ultramafic Rocks ◽  
Banded Iron Formation ◽  
Sedimentary Structures ◽  
The North ◽  
Gneiss Complex ◽  
Supracrustal Belt ◽  
Silicate Rocks

A coherent stratigraphy is recognised in the highly deformed, amphibolite facies early Archaean Isua supracrustal belt. The supracrustal belt consists of layered rocks (in which sedimentary structures are locally preserved), ultramafic rocks and units of garbenschiefer (a massive Mg-Al rich, leucoamphibolite). The layered supracrustal rocks form two sequences, which are separated from each other tectonically. When folding is taken into account, these sequences are now less than 200 m thick. Sequence A forms most of the belt. In it there is a transition upwards from predominantly layered amphibolites with banded iron formation horizons to calc-silicate rocks, carbonates and layered felsic metasediments. Sequence B is restricted to the western edge of the eastern part of the supracrustal belt. It changes upwards from predominantly layered felsic metasediments to ferromagnesian mica schists. The supracrustal belt is regarded as a thin fragment from a thicker, more extensive volcanosedimentary pile. The early Archaean gneisses adjacent to the supracrustal belt consist of early multiphase tonalites which were first intruded by mafic dioritic dykes and then by granitic sheets. The granitic sheets were originaIly horizontal to gently inciined and form up to 40 per cent of the gneiss complex. Interdigitation of supracrustal rocks and gneisses in the Isukasia area is due to both the style of intrusion ofthe gneisses and to tectonic intercalation. Archaean basic dykes that cut the supracrustal belt and adjacent gneisses are ofseveral generations. Within and south of the supracrustal belt they are generally strongly deformed and have been recrystallised under amphibolite facies conditions; but in the north of the area they are generally better preserved. The dykes cut across several generations of structures in the supracrustal belt and the adjacent gneisses.

scholarly journals IDADE U-Th-Pb DA MONAZITA E CORONAS DE REAÇÃO FOSFATO-SILICATO DE METACHARNOENDERBITO NEOARQUEANO DO SUL DO CRÁTON SÃO FRANCISCO (MG)

2016 ◽  
Author(s):  
Daniel Andrade Miranda ◽  
Alexandre de Oliveira Chaves
Keyword(s):  
Electron Microprobe ◽  
Granulite Facies ◽  
Amphibolite Facies ◽  
Metamorphic Fluids ◽  
Phosphate Silicate ◽  
Chemical Dating

ResumoNa porção Sul do Cráton São Francisco (MG), a oeste da cidade de Bom Sucesso, ocorrem litotipos neoarqueanos metamorfizados que variam desde termos ultramáficos, gabro-noríticos, enderbíticos a charnockíticos, e graníticos. Proveniente desta associação, um metacharnoenderbito cristalizado e metamorfizado em fácies granulito por volta de 2700 Ma, guarda cristais de monazita com coronas de apatita, allanita e epidoto surgidas pela interação da monazita com fluidos metamórficos tardios contendo Ca, Fe, Si e Al. Através da microssonda eletrônica, as composições dos cristais de monazita foram determinadas e seus teores de U, Th e Pb permitiram a obtenção de uma idade química neoarqueana média de 2657 ± 36 Ma. Sugere-se que ela corresponda à idade do retrometamorfismo de fácies anfibolito do metacharnoenderbito desenvolvido durante o período tardi-colisional Neoarqueano do evento Rio das Velhas, momento durante o qual as coronas de reação fosfato-silicato teriam se desenvolvido contemporaneamente ao crescimento de anfibólio e biotita da referida rocha.Palavras Chave: monazita, datação química U-Th-Pb, coronas de reação fosfato/silicato, Neoarqueano, Cráton São Francisco.AbstractMONAZITE U-Th-Pb AGE AND PHOSPHATE-SILICATE REACTION CORONAS OF A NEOARCHEAN METACHARNOENDERBITE FROM SOUTHERN SAO FRANCISCO CRATON (MG). In the southern portion of the São Francisco Craton (MG), west of the Bom Sucesso city, neoarchean metamorphosed lithotypes outcrop, which include ultramafic bodies, gabbro-norites, enderbites to charnockites, and granites. From this association, a metacharnoenderbite crystallized and metamorphosed under granulite facies around 2700 Ma yielded monazite crystals with apatite, allanite and epidote coronas arising due to the interaction of monazite with metamorphic fluids containing Ca, Fe, Si and Al. By electron microprobe, an average chemical age of 2657 ± 36 Ma was obtained. It is suggested that it corresponds to the age of amphibolite facies retrometamorphism developed during the Neoarchean late-collisional period of the Rio das Velhas event, during which time the phosphate-silicate reaction coronas would have developed contemporarily to the growth of amphibole and biotite in such rock.Keywords: Monazite, U-Th-Pb chemical dating, phosphate/silicate reaction coronas, Neoarchean, São Francisco Craton.

METAMORPHISM OF THE MEGUMA GROUP OF NOVA SCOTIA

1966 ◽  
Vol 3 (7) ◽  
pp. 959-974 ◽  
Author(s):  
F. C. Taylor ◽  
E. A. Schiller
Keyword(s):  
Nova Scotia ◽  
Regional Metamorphism ◽  
Greenschist Facies ◽  
Amphibolite Facies ◽  
Contact Metamorphism ◽  
Granitic Rocks ◽  
Structural Elements ◽  
Early Ordovician ◽  
Quartz Veins ◽  
Granite Emplacement

The Meguma group of lithic greywacke, feldspathic quartzite, slate siltstone, and argillite is Early Ordovician or older in age and has undergone both regional and contact metamorphism. Both types of metamorphism have resulted in recrystallization and locally in orientation of newly formed minerals. Metasomatism and retrogressive metamorphism are subordinate and only locally important. Regionally metamorphosed rocks are divided into greenschist and almandine–amphibolite facies, although some assemblages cannot be assigned with certainty. Locally, biotite and garnet isograds are mappable within the greenschist zone.Relationships between regional metamorphism and structural elements (folding) show that deformation preceded regional metamorphism. Intrusion of granitic rocks has produced a zone of contact metamorphism (hornblende–hornfels facies) that is superimposed upon regional greenschist facies rocks, which shows that granite emplacement occurred after the regional grade was reached. Gold–quartz veins are confined to areas lying in the greenschist zone of regional metamorphism, which suggests that the almandine–amphibolite zone is not favorable.

Mineralogy and Petrology of Serpentine

2007 ◽  
Author(s):  
Earl B. Alexander ◽  
Roger G. Coleman ◽  
Todd Keeler-Wolfe ◽  
Susan P. Harrison
Keyword(s):  
Ultramafic Rock ◽  
Magnesium Silicate ◽  
Ultramafic Rocks ◽  
Chemical Compositions ◽  
Silicate Minerals ◽  
Excess Iron ◽  
Serpentine Minerals ◽  
Similar Chemical ◽  
Serpentine Mineral ◽  
Mineralogical Compositions

“Serpentine” is used both as the name of a rock and the name of a mineral. Mineralogists use “serpentine” as a group name for serpentine minerals. Petrologists refer to rocks composed mostly of serpentine minerals and minor amounts of talc, chlorite, magnetite, and brucite as serpentinites. The addition of “-ite” to mineral names is common practice in petrologic nomenclature. For instance, quartzite is a name for a rock made up mostly of quartz. Serpentinites are rocks that form as a result of metamorphism or metasomatism of primary magnesium–iron silicate minerals. This entails the replacement of the primary silicate minerals by magnesium silicate serpentine minerals and the concentration of excess iron in magnetite. “Mafic” is a euphonious term derived from magnesium and ferric that is used for dark colored rocks rich in ferromagnesian silicate minerals. “Ultramafic” is used when the magnesium–ferrous silicate minerals compose >90% of the total rock. Olivine, clinopyroxene, and orthopyroxene are the minerals in primary ultramafic rocks, with minor amounts of plagioclase, amphibole, and chromite. Ultrabasic has been used by some geologists in referring to ultramafic rocks. The most common ultramafic rocks are harzburgite, containing <75% olivine and 25% orthopyroxene; dunite, with 100% olivine; and lherzolite, which has 75% olivine, 15% orthopyroxene, and >10% clinopyroxene, with or without plagioclase. Very small amounts of chromite are present in all of the mantle ultramafic rocks (Coleman 1971). The alteration of primary ultramafic rocks to serpentine mineral assemblages is incremental due to episodic invasion of water into the ultramafic rock. It is difficult to distinguish and map the gradations from primary ultramafic rock to serpentinite. Because of this difficulty in distinction, we prefer to use the term ultramafic or serpentinized peridotite for all gradations to serpentinite. Pedologists and botanists commonly group serpentinites with primary ultramafic rocks and refer to these substrates as serpentine because all of them have similar chemical compositions. As will become apparent later, there is great variability in the mineralogical compositions of these rocks and the soils derived from them.

scholarly journals Late Cretaceous to Paleocene Tectonometamorphic Evolution of the Blanchard River Assemblage, Southwest Yukon: New Insight into the Terminal Accretion of Insular Terranes in the Northern Cordillera

Lithosphere ◽  
2020 ◽  
Vol 2020 (1) ◽  
Author(s):  
Lianna Vice ◽  
H. Daniel Gibson ◽  
Steve Israel
Keyword(s):  
British Columbia ◽  
Late Cretaceous ◽  
Amphibolite Facies ◽  
Contact Metamorphism ◽  
Northern Coast ◽  
Coast Mountains ◽  
Tectonic Events ◽  
Western Cordillera ◽  
History Of ◽  
Northwestern North America

Abstract The Intermontane-Insular terrane boundary stretches over 2000 kilometers from British Columbia to Alaska in the western Cordillera. Juxtaposed between these terranes is a series of Jura-Cretaceous basinal and arc assemblages that record a complicated and contested tectonic evolution related to the Mesozoic-Paleocene accretionary history of northwestern North America. In southwest Yukon, west-verging thrust faults facilitated structural stacking of the Yukon-Tanana terrane over these basinal assemblages, including the Early Cretaceous Blanchard River assemblage. These previously undated compressional structures are thought to be related to the final collapse of the Jura-Cretaceous basins and the tectonic burial of the Blanchard River assemblage resulting in amphibolite facies metamorphism. New in situ U-Th-Pb monazite ages record at least three tectonic events: (1) the tectonic burial of the Blanchard River assemblage to amphibolite facies conditions between 83 and 76 Ma; (2) peak burial was followed by regional exhumation at ca. 70-68 Ma; and (3) intense heating and ca. 63-61 Ma low-pressure contact metamorphism attributed to the intrusion of the voluminous Ruby Range suite, which is part of the northern Coast Mountains batholith. The tectonometamorphic evolution recorded in the Blanchard River assemblage can be correlated to tectonism within southwest Yukon and along the length of the Insular-Intermontane boundary from western British Columbia through southwestern Yukon and Alaska. In southwest Yukon, these results suggest an asymmetric final collapse of Jura-Cretaceous basins during the Late Cretaceous, which relates to the terminal accretion of the Insular terranes as they moved northward.

scholarly journals GEOLOGIA DA REGIÃO DE JEQUERI-VIÇOSA (MG), ORÓGENO ARAÇUAÍ MERIDIONAL

2013 ◽  
Author(s):  
Daniel Tavares Gradim ◽  
Gláucia Nascimento Queiroga ◽  
Tiago Amâncio Novo ◽  
Carlos Maurício Noce ◽  
Antônio Carlos Pedrosa-Soares ◽  
...  
Keyword(s):  
Partial Melting ◽  
Shear Zone ◽  
Granulite Facies ◽  
Minas Gerais ◽  
Amphibolite Facies ◽  
Ultramafic Rocks ◽  
Metamorphic Rocks ◽  
The West ◽  
Minas Gerais State ◽  
Araçuaí Orogen

RESUMO: A característica fundamental da região de Jequeri-Viçosa, situada no extremo sul do Orógeno Araçuaí, é a abundância de rochas metamórficas, ortoderivadas e paraderivadas, de fácies anfibolito alto e granulito. O embasamento paleoproterozóico é representado, a oeste, por ortognaisses tonalíticos a graníticos do Complexo Mantiqueira e, a leste, por ortognaisses charno-enderbíticos do Complexo Juiz de Fora. Ambos os complexos incluem anfibolitos e exibem intensidades variáveis de migmatização. O contato entre eles é marcado pela zona de cisalhamento transpressiva destral de Abre Campo, interpretada como uma sutura paleoproterozóica reativada no Neoproterozóico. O Anfibolito Santo Antônio do Grama e rochas meta-ultramáficas associadas (Córrego do Pimenta) representam restos ofiolíticos ediacaranos, colocados ao longo da Zona de Cisalhamento de Abre Campo. Assentada sobre o embasamento, na parte oeste da área, ocorre uma associação metavulcano-sedimentar neoproterozóica do Grupo Dom Silvério, composta por xistos diversos e quartzito. Na porção leste da área mapeada, a cobertura metassedimentar neoproterozóica é atribuída ao Grupo Andrelândia que inclui paragnaisse migmatítico e raro quartzito. Corpos de hidrotermalito quartzoso, indiscriminadamente associados às unidades do embasamento e da cobertura neoproterozóica, ocorrem ao longo de zonas de cisalhamento. Hidrotermalitos ferruginosos associam-se ao Complexo Mantiqueira na Zona de Cisalhamento de Ponte Nova. O granito foliado a milonitizado da Serra dos Vieiras parece ser um produto de fusão parcial do paragnaisse Andrelândia. Completam o quadro geológico os pegmatitos da Suíte Paula Cândico e diques de diabásio mesozóicos.Palavras-chave: Paleoproterozóico, Neoproterozóico, Orógeno AraçuaíABSTRACT: GEOLOGY OF THE JEQUERI-VIÇOSA REGION, MINAS GERAIS STATE, SOUTHERN ARAÇUAÍ OROGEN. This paper focuses on the southwestern sector of the Araçuaí orogen in a region located close to the boundary with the northern Ribeira orogen. This region is rich in ortho- and para-derived metamorphic rocks of the high amphibolite and granulite facies. The Paleoproterozoic basement includes, to the west, tonalitic to granitic orthogneisses of the Mantiqueira Complex and, to the east, enderbitic to charnockitic orthogneisses of the Juiz de Fora Complex. Both complexes also include amphibolite enclaves and show several rates of partial melting. The contact between them is marked by the dextral transpressional Abre Campo shear zone, considered to be a Paleoproterozoic suture reactivated during the Neoproterozoic Era. The Santo Antônio do Grama Amphibolite and associated meta-ultramafic rocks (Córrego do Pimenta) are Ediacaran ophiolite slivers emplaced along the Abre Campo shear zone. In the western part of the region, the Paleoproterozoic basement is locally covered by a metavolcano-sedimentary assemblage composed of amphibolite facies schist and quartzite of the Neoproterozoic Dom Silvério Group. To the east, the Neoproterozoic cover comprises the migmatized paragneiss and rare quartzite of the Andrelândia Group. The Serra dos Vieiras foliated to mylonitic granite seems to be formed from the partial melting of the Andrelândia paragneiss. Pegmatites of the Paula Cândido Suite and Mesosozic diabase dikes complete the geologic framework of the mapped area.Keywords: Paleoproterozoic, Neoproterozoic, Araçuaí Orogen

scholarly journals MN-ANDALUSITE, SPESSARTINE, MN-GROSSULAR, PIEMONTITE AND MN-ZOISITE/CLINOZOISITE FROM TRIKORFO, THASSOS ISLAND, GREECE

2017 ◽  
Vol 50 (4) ◽  
pp. 2068 ◽  
Author(s):  
P. Voudouris ◽  
I. Graham ◽  
K. Mavrogonatos ◽  
S. Su ◽  
K. Papavasiliou ◽  
...  
Keyword(s):  
Sustainable Development ◽  
Greenschist Facies ◽  
Contact Metamorphism ◽  
Retrograde Metamorphism ◽  
Prograde Metamorphism ◽  
Silicate Minerals ◽  
Vein Formation ◽  
Mineral Associations ◽  
Silicate Layers ◽  
Iron Bearing

Mylonitized manganiferous schists and calc-silicate layers intercalated within amphibolite- to greenschist facies mica schists from the Trikorfo area (Thassos Island, Greece), host an unusual Mn-rich paragenesis of metamorphic silicate minerals, most of them in large, gemmy crystals. The silicates occur both in layers subparallel to the foliation and within discordant veins cross-cutting the metamorphic fabric. Piemontite (up to 12.7 wt. % Mn2O3), Mn-rich epidote (up to 7.8 wt. % Mn2O3), Mn-rich andalusite (up to 15.6 wt. % Mn2O3), Mn-poor pink clinozoisite-epidote (up to 0.87 wt. % Mn2O3), Mn-poor pink zoisite (up to 0.21 wt. % Mn2O3), spessartine (up to 47.7 wt. % MnO) and Mn-rich grossular (up to 3.6 wt. % MnO) are associated with diopside, hornblende, phlogopite, muscovite, tourmaline, hematite and iron-bearing kyanite. The studied assemblages are indicative of high fO2 conditions due to the presence of highly oxidized pre-metamorphic Mn-rich mineral associations. They developed during prograde metamorphism of a Mn-rich sedimentary protolith(s), followed by re equilibration to post-peak metamorphic conditions, vein formation and metasomatism during retrograde metamorphism accompanying the exhumation of the Thassos Island during the Oligocene-Miocene. Alternatively, the skarn similar mineralogy of the calc-silicate layers could have been formed by fluids released by granitoids during contact metamorphism. The studied area represents a unique mineralogical geotope. Its geological-mineralogical heritage should be protected through establishment of a mineralogical-petrological geopark that will also promote sustainable development of the area.

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